Safety couplings



' Feb. 19, 1957 G. BURKHARDT 2,781,882

SAFETY COUPLINGS Filed May 14, 1954 v INVENTOR GUSTA v BURKHARDT BY WWM' SAFETY COUPLINGS Gustave Burkhardt, La Garenne-Colombes, FranceApplication May 14, 1954, Serial No. 429,945

Claims priority, application France May 15, 1953 8 Claims. (Cl. 192-56)My invention relates to safety couplings of the general type adapted totransmit a drive torque from a drive to a drive member so long as thetorque to be transmitted has not exceeded a predetermined value, butwhich will disengage the drive transmission when said value is exceeded,in order to prevent damage to the operating parts.

In many cases it is found desirable that the coupling be capable duringa starting-up period of transmitting a torque substantially greater thanthat which is normally permissible during the steady operating conditionor at full speed.

It is, accordingly, :1 main object of the invention to provide asafetycoupling which will disengage automatically under loads higherthan a predetermined load at speeds in excess of a predetermined speed,and yet will not disengage under similar loads at lesser speeds.

Another object is to provide an improved safety coupling which, onattainment of a predetermined angular speed, will be made effective todisengage automatically on occurrence of slippage between the coupledmembers.

A further object is to provide a safety coupling which on attainment ofa predetermined angular speed will be made effective to disengageautomatically on subsequent occurrence of slippage between the coupledmembers, and which will thereafter retain its effective condition untilthe angular speed has dropped to a value substantially lower than saidpredetermined speed.

A further object is to provide an improved safety coupling which willpermit starting under overload conditions.

A further object is to provide an improved safety coupling of theabove-specified type adapted for instantaneous reengagement.

Further objects together with the features and advantages of theinvention will appear as the disclosure proceeds.

An exemplary embodiment 'of the invention will now be described withreference to the accompanying diagrammatic drawings, by way ofillustration but not of limitation.

In the drawings:

Fig. 1 is an axial sectional view of an improved coup Fig. 2 is a crosssection on line 2-2'of Fig. 1;

Fig. 3 is a section :on line 33 of Fig. 1;

Figs. 4 and 5 are sectional views, on an enlarged scale of a yieldingconnecting element respectively in the undistorted and distortedcondition.

As shown, a drive shaft 1 and a driven shaft 2 are inter-connected by aneedle coupling assembly of the socalled Stieber type, as disclosed forexample in French Patent 807,248, filed June 9, 1936. Such ,a couplingis capable of transmitting acomparatively high torque with only a verylow degree of pressure between the coupling members. For this purpose,the drive shaft 1 has secured coaxially with it a bushing 3a. A furtherbushing 3 shown as surrounding the bushing 3a for a purpose to ireStates Patent ice be described later may for the present be consideredas forming an integral part with the bushing 3a. Similarly secured onthe driven shaft 2 is a bushing 4. Shown as interposed between shaft 2and bushing 4 is a bushing 4a to be later described and which maytemporarily be regarded as integral with the bushing 4. The bushing 4surrounds the bushing 3 in slide-fit engagement With it andlongitudinally extending slots are preferably formed in the bushing 4 tofacilitate the engagement. Surrounding the bushing 4 is a furtherbushing or sleeve 5 also formed with one or more slots for tightengagement of sleeve 5 around bushing 4. The sleeve 5 has a slightlytapered outer periphery to serve as an inner race for a needle bearingcomprising the needles 6 retained by means of a cage 7. Said needles, inaddition to being conically inclined with respect to the axis of theshafts, are offset or twisted a small angle with respect to the axis ofthe shafts, as is conventional in a Stieber coupling. An outer race isprovided for the needle bearing by a ring 8 having an inner surfaceformed with a complementary taper to that of the inner race member 5.Because of the inclination of the twisted needles 6, a difference of thespeeds of rotation of the drive shaft and the driven shaft in onedirection will cause the ring 8 to be moved onto the sleeve 5 with ascrew-like action, while relative movement between the shafts in theopposite direction will cause the ring 8 to be unscrewed.

, To clamp the above described structure in assembled relationship theouter ring 8 is rotated in a direction reverse from the normal notationof the drive and driven shafts. Because the needles 6 are twisted withrespect to the axis of the shafts, the ring 8 will be moved onto thering 5. The rotation of ring member 8 is limited by means of a nut 9 anda locknut 9a engaging a threaded portion of the outer periphery of ring8, the nut 9 being adapted to be blocked against a shoulder 41) orflange 4b formed on the driven bushing 4. In this way the de gree ofclamping engagement between the members of the assembly can be adjustedas desired. The locknut 9a fixes the position of nut 9. The structure sofar described comprises a conventional Stieber coupling as disclosed forinstance in the afore-mentioned patent.

According to a feature of the present invention the bushing assembly3-3a associated with drive shaft 1 has a number of equispaced pins 10projecting axially therefrom in the rearward direction (toward shaft1'); while four pins 10 are shown herein, any other suitable number maybe used. Two diametrically opposed ones of the pins 10 each have acentrifugal element or pawl 11 freely pivoted thereon, see Fig. 2, whilethe other diametrically opposed pair of pins 10 have cooperating lockingfree members 12 freely pivoted thereon. Between one end of each pawl 11and the adjacent end of the adjacent locking member 12 a spring 13 isinterposed. The springs 13 tend to urge the pawls and members to therelative condition illustrated in the lower part of Fig. 2, which is theidle condition.

Secured to the outer periphery of outer ring member 8 is an annulus 14internally formed with equispaced projections or teeth 14a. The pawls 11have the end thereof remote from that abutting the springs 13 formedwith a nose portion 11a including a surface adapted to engage a side ofany one of the teeth 14a when the pawl 11 is pivoted counterclockwise(according to Fig. 2) in opposition to the action of springs 13. Thisposition of the pawl is illustrated for the upper pawl in Fig. 2.Moreover, the nose portion of each pawl 11 is formed with a concaveportion adapted, when the pawl has assumed the condition just indicated,to interlock with a complementary portion of the adjacent end of theadjacent locking member 12.

It will be noted from Fig. 2 that the configuration of the pawls 11 andlocking members 12 is such that, when the assembly is rotated,centrifugal force will tend to pivot the pawls 11 counterclockwise andthe weight members 12 clockwise, since the longer arm of the pawl illfaces the longer arm of the locking member 12. The springs 13 willresist such movement however, and the force of the springs is sopredetermined that the pawls and locking members are allowed to pivot inorder to assume the above-described interlocking condition (as shown forthe upper assembly in Fig. 2) as the speed of rotation approaches itsnormal operating value.

When in this interlocking condition the radial distance of the centre ofgravity of each pawl 11 and each member 12 from the centre of shaft 1 isincreased over the radial distance of the centre of gravity of thoseparts in the noninterlocked (inoperative) condition of the parts: at thesame time, the point of engagement of the spring 13 with the pawl andlocking member is shifted in such a direction as to reduce the leverageof the spring acting to restore the parts to their free or inoperativeposition; this reduction being especially great in respect of thelocking members 12. As a result of the foregoing effects, the pawls andlocking members are unable to return to their inoperative position untilthe speed of rotation of the structure has dropped substantially tozero.

In operation, as the drive torque exceeds the limiting value for whichthe coupling has been preset, relative slippage occurs between thebushing assembly 3--3a associated with drive shaft 1 and bushingassembly 4-4a associated with driven shaft 2. The outer clamping ring 8is at this time integrally connected for movement with the bushing 3-3aowing to the pawls 11 now being in their interlocked position with theteeth 14a of annulus 14; said ring 8 therefore will revolve somewhatfaster than the sleeve to produce a relative movement of the ring withrespect to the sleeve; because of the inclination of needles 6, this inturn causes an initial unscrewing and disengagement of the coupling andincreases the relative slippage between the drive and driven members,thereby accelerating the full release of the coupling.

Thus it will be seen that, on the one hand, the release of the couplingcannot occur until the pawls have assumed their operative interlockingcondition; hence the coupling cannot become released during the startingperiod when a higher drive torque is required to be transmitted; on theother hand, the pawls are unable to return to their initial inoperativecondition even if the speed of rotation materially decreases. Thecoupling also releases therefore if the increase in transmitted loadresults in a simultaneous decrease in speed.

According to a feature of the invention, yielding connecting elementsmay be provided. Such elements may be interposed between the bushings 4and 4a, or alternatively between the bushings 3 and 3a, or, as shown,both between bushings 4, 4a and between bushings 3, 3a.

For this purpose, recesses 2t) and 21 are formed in the bushings 4- and4:! parallel to the axis thereof. As shown in Fig. 4, each recess is aportion of a cylinder of circular cross section. The circular crosssections of recesses 20 and 21 are preferably equal in radius but havetheir centres displaced, as shown in the figure so that the arcconstituting the cross section of each recess 20 or 2.1 subtends anangle of somewhat less than 180.

Received in the housing formed by each pair of recesses 2.0, 7.1 is aspring 22, e. g. as shown a spiral spring of substantial width in theaxial direction, so that each spring may correspond in length to thelength of the recesses or to a substantial fraction of said length. Inthe rest condition, these springs have the undistorted shape visible inFig. 4. When however the bushing 4a is displaced relative to the bushing4 in the direction of the arrow x in Fig. 5 the springs become distortedbetween the cylindrical walls of the recesses thereby providing ayielding connection between the bushings. A similar yielding connectionis provided between the bushings 3 and 3a; the associated recesses areclearly shown in Fig. 1.

It will be understood that many different embodiments of the inventionmay be designed other than the single embodiment shown. Thus it will beevident that the pawls 11, 12 might be pivoted to a part connected withthe annulus 14, while the teeth 14 would then be provided on the hub 23keyed to the drive shaft 1.

What I claim is:

1. In a coupling for a drive and a driven shaft, the drive shaft havinga sleeve integral therewith and the driven shaft having a sleeve with aconical surface integral therewith fitting over the sleeve of the driveshaft, a tightening ring having an interior conical surfacecomplementary to the conical surface on the driven shaft sleeve, aplurality of needle roller bearings positioned between said conicalsurfaces at an angle to the axis of said shafts, whereby on rotation ofsaid tightening ring in a direction opposite to the direction ofrotation of the shafts the tightening ring is tightened onto said drivenshaft sleeve, and a cage to hold said hearings in position, thatimprovement comprising means on said drive shaft operable at apredetermined speed to lock said tightening ring to said shaft, andmeans on said drive shaft acting on said locking means to retain saidlocking means in the locked position.

2. The improvement as claimed in claim 1 in which said means for lockingthe drive shaft to said tightening ring at a predetermined speed of thedrive shaft comprises a plurality of pawls pivoted on said drive shaft,an annulus fixed to said tightening ring and surrounding said pawls andhaving a plurality of inwardly projecting teeth, said pawls coming intoengagement with the teeth under the action of centrifugal force at apredetermined speed of said drive shaft.

3. The improvement as claimed in claim 1 in which said retaining meanscomprise a plurality of small mass-cs pivoted on the drive shaft andpositioned to swing outwardly and engage said locking means under theaction of centrifugal force.

4-. The improvement as claimed in claim 1 in which said means forlocking the drive shaft to said tightening ring at a predetermined speedof the drive shaft comprises a plurality of pawls pivoted on said driveshaft, an annulus fixed to said tightening ring and surrounding saidpawls and having a plurality of inwardly projecting teeth, said pawlscoming into engagement with the teeth under the action of centrifugalforce at a predetermined speed of said drive shaft, and in which saidretaining means comprise a plurality of small masses pivoted on thedrive shaft and positioned to swing outwardly and engage under the endsof the pawls engaging the teeth of the tightening ring under the actionof centrifugal force.

5. The improvement as claimed in claim 4 in which said pawls and smallmasses are pivoted with their pivoted ends opposed to each other, saidretaining means further comprising a plurality of springs which aredisposed between the opposed pivoted ends of the pawls and the smallmasses, said springs being of such strength that the pawls and the smallmasses are moved towards the annulus by centrifugal force to engage theteeth only when the speed of the drive shaft reaches a predeterminedvalue, the form of the ends of the pawls and the small masses engaged bysaid springs being such that the springs cannot force the pawls and thesmall masses out of the locking position until the speed of rotation ofthe drive shaft becomes very small.

6. In a coupling as claimed in claim I, that further improvementcomprising means to elastically couple said shafts, said means extendingparallel to the axis of the shafts and being positioned between thedrive shaft and the sleeve thereon and the driven shaft and the sleevethereon.

7. The improvement as claimed in claim 6 in which said means forelastically coupling the shafts comprise References Cited in the file ofthis patent UNITED STATES PATENTS Proctor Mar. 25, 1919 Rigolage Nov.20, 1928 FOREIGN PATENTS France May 9, 1941

